Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Website Speed Ranker - Compare how fast your website loads vs your competitors
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Textalyzer - Analyze text readability and SEO parameters
Better Uptime - We call you when your website goes down
SanityCheck - Get the exact data you need from Google Search Console.